1. Field of the Invention
The present invention relates to a mechanism for moving goods, particularly to a robot manipulator, a structure and a structure control system used therefor.
2. Description of the Related Art
In recent years, the shortage and aging of the working population resulting from the falling birthrate and aging population have been predicted and robots for industry use and home use to compensate therefor have been expected. Particularly, manipulators and the like capable of gripping various goods are essential and important to do complicated operations. Various considerations are made on the application of these manipulators as artificial arms for people with disabled hands.
FIGS. 15 and 16 are diagrams showing a conventional manipulator disclosed in Japanese Unexamined Patent Publication No. S61-249296. In FIG. 15, identified by 803, 804 are arms, by 805 a hand device, and by 806 a work gripped by the hand device 805. FIG. 16 shows a safety device 807 of this manipulator provided in a connected part between the arm 804 and the hand device 805. The safety device 807 includes a first base 807a connected to the arm 804, a second base 807b and a supporting shaft 807i connecting the second base 807b relatively rotatable with respect to the first base 807a. 
The hand device 805 is connected with the second base 807b. A pin 807a penetrates from the first base 807a to the second base 807b. Thus, normally, the second base 807b does not relatively rotate with respect to the first base 807a. Further, an insertion hole for the pin 807c is closed by a bolt 807d to prevent the pin 807c from dropping.
If a work 806 collides with an external object, the pin 807c is sheared by a resulting impact, whereby the second base 807b becomes rotatable with respect to the first base 807a. Since the hand device 805 and the work 806 become rotatable about the supporting shaft 807i, the transfer of kinetic energy to the hand device 805 when the object collides with the arms 803, 804 is prevented, whereby the breakage of the hand device 805 can be prevented.
However, the safety device of the conventional manipulator had the following problems. Specifically, if an object collides on an extension of the supporting shaft 807i, the pin 807c is not sheared. Thus, the safety device 807 does not function. Further, if an object collides with the arms 803, 804, the total masses of the arms 803, 804 act on the colliding object. Thus, if a person collides, danger is predicted.